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This blog is about speculative biology. Recurrent themes are biomechanics, the works of other world builders, and, of course, the planet Furaha.

Sunday, 22 January 2012

The eyes have it!

I guess almost everyone who designs fictive alien life forms want them to look truly 'alien': you want your animal to have something that tells the viewer that this is an original; it should look unearthly and yet as if it ought to look that way. The word 'alienness' is perhaps grammatically correct, but lacks punch; something like 'alienosity' might do the trick...

Frivolity aside, striking a balance between oddity and plausibility is difficult. Darwinian evolution tends towards optimisation, which in reality means the optimal balance between function and cost; economy of design pervades everything in biological evolution. As evolution on Earth has been following that path for quite some time, it is not easy to come up with strikingly different designs that work at least as well as familiar ones.

Doing away with eyes is such a major departure from 'earth standard', increasing alienosity significantly. Imagine sightless animals with otherwordly senses, pinging your innards with sonar or recognising you by the thermal pattern of your warm throat, your cold nose and old hair. Yes, sightlessness fits the bill nicely. But can you do away with eyes? I think not, except under very special circumstances. I will try to discuss why 'the eyes have it', and this will probably need more than one post. The present one will deal with probably the most famous sightless speculative world: Darwin IV by Wayne Douglas Barlowe.

Let me start by stating my admiration for Mr Barlowe's painting skills. The pronghead, show above, works great against the background, and the fact that is half lit works compositionally and also highlights the luminescent spots nicely. I have said it before: I wish I could paint as well. Darwin IV is presented in his book 'Expedition', available from Amazon. A television documentary with computer generated graphics is available as well.

The picture here shows some ballooning animals floating away in the darkness (they are called 'eosapien', but I suspect that that is a mistake caused by the idea that the 's' in 'sapiens' denotes a plural, but it does not -the plural would be 'sapientes'-). The luminescent spots are well visible on these animals as well as on animals in the distance. Perhaps the latter ought to be less conspicuous, seeing that the eosapiens are predators.

There is an explanation in the beginning of the book 'expedition' explaining why animals there have no eyes. The idea is that the planet was covered in thick fog for very long periods, so that vision as we know it was pretty useless during that time. Animals accordingly developed other senses: apparently there is a pressure-sensitive lateral line system, but not much is known about it. Also stated are the ability to use sonar and infrared, and the latter one is the subject of this post. The infrared sense is apparently located in 'tiny infrared receptor pits'. When the atmosphere cleared up later, these alternate senses were so well developed and entrenched that vision did not have much chance: the first stages of eyes would be poor, and would not convey an appreciable advantage to their owners, so their evolution never got under way. As defences go, this is an ingenious one. I doubt eye evolution would really be held back by superior senses, already present, but that line of thought deserves further thought.

First, let's discuss the heat sense, one of Darwin IV's ways of making sense of the environment. Many of Barlowe's animals have intriguing dots and stripes in glorious colours, glowing in the dark. Now bioluminescence was a brilliant idea with a high alienosity index ( I wish I had thought of that in time). However, it is rather odd for animals to have organs that produce light when there is nothing around to see that light. At first sense offering light to the blind seems a serious mistake, but the text again shows that this critique has been foreseen. It states that these 'biolights' are 'heat-radiating bioluminous spots that appear quite vivid to infrared sensors'. In effect, this means that the production of light is a side effect of the production of heat.

Electromagnetic spectrum from Wikipedia

Here we need to call attention to the electromagnetic spectrum. You may remember that the part humans can see is flanked by ultraviolet on the high frequency side and by infrared on the low frequency side. Now infrared is divided into near infrared and far infrared. Near infrared is in effect another colour, one humans simply cannot see, but which does not represent heat as such (here is a nice photography site explaining it well).

There are many images on the internet taken in the near infrared range, 'translated' to activity in the part of the spectrum we can see (a true infrared image is useless, as we wouldn't even see that there was an image!). Many images of woods and trees show that leaves are very bright in the near infrared range, but that does not mean they are warm. They are not; they simply reflect a lot of the near infrared radiation falling on them, coming from the sun (the sun shines brightly in the near infrared range). Remember that a green leaf looks green because it reflects more green light than it does light of other colours. By the way, the images above show that near infrared travels better through haze and fog than visible light does, so having fog as part of the 'anti-eye argument' has its merits.

But do the animals of Darwin IV make use of near infrared? The text states that we are dealing with detection of heat, and that means 'far infrared'. Then again, most objects radiating heat also radiate near infrared radiation, so you could use one for the other. But I will assume true heat detection.

The heat organs on the bodies of Darwin IV's animal also produce visible light. That is not surprising: any fire produces heat as well as light, and often both effects are welcome (come to think of it, a fire that produced heat but not visible light would be pretty dangerous). Light bulbs are only meant to produce light, but are spectacularly inefficient in this respect: most of the power they consume goes into the generation of heat rather than of light. Nature, however, has managed to produce light without heat in the form of bioluminescence. That separation holds on Earth, though. On Darwin IV, you would expect evolution to be faced with the challenge of producing heat as efficiently as possible, meaning without squandering resources such as producing visible light as a side effect. Apparently evolution failed in this respect. This seems rather unlikely, as there must be metabolic ways to produce just heat but not light in a controlled manner. Our own bodies radiate heat but not light, so I do not think that bioluminescence as a by-product of heat production is very convincing.

But the production side of heat signals is not my major concern; that resolves around the reception side: how do Barlowe's animals make sense of the heat signature of other animals? As usual, there are animals on Earth making use of heat detection; the pit viper is probably the most famous one***. This involves making sense of radiation in the far infrared range, something called 'thermography', or writing with heat. I have copied some images from Wikipedia below. There is a good discussion here as well.

Thermography of a cat from Wikipedia

The main point of these images is what they are: images! An image shows you what is where in space. The more pixels you have, the more information the image can carry. An image is made by a camera, and digital cameras have a receptive surface, and the image is focused on that surface by a lens. A cheap camera might have a poor lens, with an unsharp picture, and with a low number of pixels. When better quality is asked for, lenses get better and the number of pixels increases. The above, in a nutshell, is the evolution of the eye (well, not every eye resembles a camera, but many do). Man-made thermographic images show that the radiation of the far infrared basically follows the same principles as visible light does. You can bend rays with a lens, and you can detect them with dedicated sensors. That does not hold for all parts of the electromagnetic spectrum: it would be hard to detect X-rays as they easily pass through tissues, and it is extraordinarily hard to focus them. I would not be surprised at all to find that biological chemicals are better at bending radiation in the visible part of the spectrum than in the far infrared: water bends light. But the premise of Darwin IV was that animals there are able to detect heat, like the pit viper. In such snakes, heat detection still has poor spatial resolution, probably because their heat detecting organs have no lens in them. Suppose the animals of Darwin IV started out a long time in their past with some molecule that responded when subjected to far infrared radiation. Wouldn't evolution drive that organ to become ever better at telling where the radiation was coming from? That development would run exactly parallel to the evolution of the eye. 'Normal' eyes started out that way, and recent evolutionary theory holds that eyes developed many times, in many forms, and extremely quickly too. The ability to detect heat would probably also be subject to the same optimisation process that affected normal vision, so its product would be an eye. Sensitive to other parts of the spectrum than our eyes, but an eye nevertheless...

24 comments:

one way to make alien life visual alien would be to explore alternate eye structures. for example, on earth the compound eye is limited to Arthropods. giving alien equivilents of mammals, reptiles, or birds compound eyes is a quick way to make them more alien. especially if you use eyes like Stomatopods, and let them see several different kinds of light with them, and/or have each eye move and focus seperately.

that was something i loved about the critters in Warren Fahy's Fragment. the description of how their compound eyes scanned left/right and up/down totally independantly 'like a mars rover' was such a creepy and alien image that a shiver ran down my back on reading it.

The word 'alienness' is perhaps grammatically correct, but lacks punch; something like 'alienosity' might do the trick...

By favorite term for the concept was "otherness," coined by David Brin. The application may seem a bit broad for some, but I think it fits the bill nicely.

By the way, the images above show that near infrared travels better through haze and fog than visible light does, so having fog as part of the 'anti-eye argument' has its merits.

Perhaps you'll be exploring more of this point in a future blog, but I've come to the conclusion that such a situation on a foggy planet would lead to a case of visual hypertrophy rather than atrophy, with the aliens visual spectrum skewing into near infrared wavelengths. Perhaps in some species this would result in the complete loss of previously evolved eyes in favor of some other sense organ, but other species could just as easily evolve more powerful eyes better suited for the hazy environments. There just isn't much justification for a wholesale loss of eyes, IMO.

Also, I begin to wonder about the generation of the heat spots. That would probably require that such species are endothermal, right? If not, is it possible for an otherwise ectothermal creature to evolve these pits as a survival trait in cold environments? Could this be a defense for a concept I had of generating heat in non-metabolic ways?

I also like how you concluded by showing the evolutionary inevitability of an eye. Whether it's the sophisticated, high resolution organ of the eagle or the poorly imaging pits of the viper (or Darwinian eosapien) the result is, one way or another an eye.

I too enjoyed the unique visual capabilities of the Fragment creatures. Do you think that another truly alien possibility would be, rather than multipurpose eyes or an "eyeless" world, to have multiple eyes specialize to different wavelengths or purposes? It's something I've explored in Nereus, particularly with the banana streak, but I wonder if multiple eyes could develop into more complex arrangements, challenging the notion that "two is better than three". What are thoughts on this front?

Considering how well water absorbs infrared light, IR eyes might still be very alien compared to visible-light eyes; whatever the lenses were made out of, unless they were quite small I would imagine that they'd need to be dry. Something like the trilobites' calcite eyes would probably work best, and calcite might even end up as the material of choice, considering its decent IR transmittance.

On the subject of eyes that appear alien...how about fresnel lenses to focus light, rather than normal lenses? It's a little difficult to imagine why exactly an organism would evolve them, as the main reason that we humans put up with the reduced image quality is so that the mass or volume of the lens can be decreased--and in animals, eyes typically aren't bulky enough for that to be a problem. Hm. Maybe for a creature that had few predators, but was still under evolutionary pressure to increase its physical size (dermal oxygen exchange in anoxic-yet-well-lit waters? Seems like an unlikely scenario).

@Evan Blacki don't see why an alien creature couldn't evolve such a thing. from what i understand, the compound eyes of stomatopods are similalry adapted, with several 'bands' of eyes in each, each band specialized in seeing a different set of wavelengths and polarizations. apparently this eye structure also gives each eye seperate trinocular focus too..

the main question becomes whether the alien eyes in question evolved at the same time and then specialized (which would limit your wavelength options), or one set developed first and later the other more specialized eyes developed.

@Ronani could see fresnel lenses evolving from transparent scales. how pluasible it is who knows though.another possible approach might be the pinhole camera.. http://en.wikipedia.org/wiki/Pinhole_cameraan animal with a solid shell having such 'eyes' might not even have visable sight organs, but still be able to see.

Mithril: You are quite right, and I can unashamedly say that that is the very reason why most Furahan life forms have compound eyes. I have been planning to write more about them, as I suspect that compound eyes, much larger than insects' ones, coupled with subtle neural programming, should allow better resolution than mere enlargement alone (but I need more proof of that).

Rodlox: For the purpose of being 'seen' by others it does not really matter whether heat is generated internally or externally, I would think? Or am I missing your point? ET is indeed a nice example...

Evan: 'otherness' is good, but for me it might also mean just another culture; it does not seem as far-ranging as I would prefer. You are quite right about expanding the visual spectrum as a solution. In fact, in the first drat of the post I had written that a pure near-infrared vision would probably result, through mutation and selection, of receptors becoming sensitive to 'new' wave lengths, in this case those of visible light. Your question about heat spots is interesting. I do not know whether their presence automatically points to endothermy. I like the idea of an ectothermal animals developing specific heat-producing organs instead of heat production being produced just about everywhere in its body as in our kind of endotherms. Such organs could be turned on and off if necessary. I would not put them on the outside of the organism though, but on the inside, with the ability to shunt arterial blood through them in an additional circulatory loop, so the 'hot blood' could transport heat through the body. Did you take the concept that far already? If not, let's patent it... And I do not think the inevitability of eyes has been proven yet in his post. At present I would say that heat detection ought to lead to an eye, but that is not the whole story yet.

Evan 2: well, various animals on Earth already have eyes specialised for different functions (spiders), and in part to different wavelengths (stomatopods), so I personally see no problem there.

Ronan: you are right in saying that the visual media of an eye should be adapted to the wave length it is supposed to work with: thermographic eyes should not absorb heat radiation. Crystalline lenses might be needed, as you say.

Mithril / Ronan / Spugpow: I like the idea of Fresnel lenses; this is ingenious, and it would work to keep lens volume down. However, remember that they only reduce lens volume, and still project light on a retina at a distance like a regular lens. So they would not reduce overall eye volume that much, and I doubt that lens volume is a big factor compared to eye volume as a whole. Still...

Trex 841: The 'visible' part of the visible spectrum indeed differs between animals, but I do not think this means you can say that the entire electromagnetic spectrum could be designated as the 'visible' spectrum. People indeed refer to the part humans can se as such, but while writing the post I thought about what constitutes vision and an 'eye', and through that 'optics'. I guess (haven't thought it through yet) that the rays in question should pass some substances (like air and water) but not all (otherwise there can be no retina) and that they should allow focusing, either by being bent or by being reflected in another direction. Others have probably already thought of such definitions. I'll look them up. You are probably referring to the 'future predator' of 'Primeval'; wasn't that a bat-derived form? I doubt that echolocation can stand in for sight, but have indeed thought that I should perhaps discuss it at some point.

'otherness' is good, but for me it might also mean just another culture; it does not seem as far-ranging as I would prefer.

Fair enough. I actually enjoy it because of its breadth in application. To me it can apply to any sort of "other" world, from the alien grandeur of Furaha to what life is like for my neighbor, a foreigner, or my brother's dog. In a sense they're all alien worlds. But to each his own.

Your question about heat spots is interesting. I do not know whether their presence automatically points to endothermy.

Yeah, I'm not sure either. There's a strong correlation, I think, because specialized infrared generators would likely evolve from more simple, generic heat generators or a widespread endothermy. The idea is intriguing to me, and as I researched the concept I found that moths in cold environments will 'shiver' before flight, effectively warming up their muscles so they can move their wings efficiently. I conceived of an organ (adapted from a couple hearts, so there's your circulatory loop) that would have a similar function, using friction for thermogenesis. However, discussion in the SE forums convinced me that fur and metabolic endothermy would be a more efficient design. "Mr. Heart-heaters" would have to eat a lot to fuel those organs, and they could easily give out. I'd still love to find out a way to make this idea happen, but I think I need to do more research on the matter and I'd love to explore it further.

About Fresnel lenses: even if they don't do much to reduce overall eye volume I think they could add their own sense of 'alienness.' Perhaps the vagaries of genetic inheritance would bring this about and make for interesting and different eyes even if there's no real advantage to them. Am I wrong in this sentiment?

"About Fresnel lenses: even if they don't do much to reduce overall eye volume I think they could add their own sense of 'alienness.' Perhaps the vagaries of genetic inheritance would bring this about..."

I can imagine fresnel lenses developing from myriads of transparent scales rather than a single mass--maybe they're the route insects would take if they evolved camera-type eyes.

Regarding compound eye resolution: perhaps the data from each eye could be compiled to create a more detailed picture, or even combined with echolocation as dolphins do to give more information about texture and density--perhaps interpreted by the visual centers as an extra "color" spectrum. Weak echolocation shouldn't be difficult to evolve; shrews do it, and even humans can with practice (could the shields of the marshwallows have a secondary role as sound-focusing structures?).

There's also scallop eyes, which apparently work like a satellite dish, in that they reflect light as opposed to refract it. Jumping spiders eyes (which I think is what the creatures of fragment's eyes were based on) have a moveable sock-like retina which they stretch in different directions to change focus and look in different directions.

With regards to the fog excuse, how much fog is enough to discredit complex eyesight, and is it an achievable amount? I ask because I designed such an alien (http://yasbp.deviantart.com/gallery/#/d4a8pki) as part of a contest, and it's one of my favorite races so far, so I really want to know if an eye-subduing perpetual mist planet is plausible enough for me to include in my project.

That is a very interesting question, perhaps deserving of a longer discussion. I will keep it short though. You could approach it from two angles:

The first is how poor visibility has to get to render vision useless. My guess is that a very thick fog on Earth reduces visibility to 5-10 meters. I suspect that adding even more droplets of water to the air than are present in such a fog would lead to the droplets coalescing, meaning they will drop to the ground as a drizzle. In other words, there may a limit to how dense a fog can get. Is a limit of, say, 5 meters enough to make vision worthless? For a dinosaur or an elephant that limit is less than or equal to one body length, and perhaps range of vision should be expressed in such terms. If so, a maximally dense fog negates the big advantage of vision, i.e. it is a long-range sense. However, I suspect that a range of 5 meters is perfectly adequate for small animals such as insects. I would not be surprised to learn that for them most relevant visual information comes from much closer by. Another argument along the same lines is that the range of vision under water is habitually much smaller than on dry land, but that has not stopped vision developing under water; quite the opposite. Finally, animals could evolve near-infrared to counter the effects of fog partially. Taken together, I think that a limited range of vision due to fog is not a good argument against vision evolving. No light at all is probably the only convincing argument (underneath an ice cap for instance).

The second angle is whether permanent fog is possible or likely. Fog is a dynamic phenomenon: forming it involves saturating air with water vapour and then altering the temperature, pressure or water content so the water condenses. From this dynamic nature it seems to me that a permanent fog seems unlikely. It also seems unlikely that fog would be present all over a planet. But perhaps you can think of a situation in which life can only evolve on a small part of the planet because of specific circumstances there, and those circumstances also involve a permanent fog rolling in from elsewhere. Even so, life had better stay confined to those areas, or else there is an excellent chance for an extremely quick evolution of vision once the animals come out of the fog.

Aww darn. Oh well, there must be other ways to make a life-bearing lightless environment, however uncommon they may be.

What about a planet with an insufficient magnetic field, so it's perpetually showered in radiation? Life could develop in underground aquifers and spread into the cave systems. However I have doubts as to whether this could lead to intelligent life.

Then there are rogue planets, but there'd be little energy, so I doubt anything could survive on one of those for long.

Perhaps the moon of a rogue planet, the tidal forces of which lead to a great amount of tectonic activity on the moon, leading to the development of plant-like thermotrophs and complex life to prey on them. The biggest problem with this is that the thermotrophs would be highly concentrated around hotspots and wouldn't grow very tall, so the animals wouldn't grow very large either. Maybe it orbits a Y dwarf instead of a rogue planet, so it has very little light emitted in addition to the heat, so both thermotrophs and photoautotrophs exist, though not enough for the animals to see anything of worth.

Or maybe the atmosphere is simply too clouded by carbon dioxide and other detritus, (like on venus, but without the acid storms), leading to an intense greenhouse effect, so the heat is more evenly distributed, and the "plants" are still forced to compete by growing over each other.

Or perhaps the dark side of a tidally-locked planet, though the dark side would be supposedly too cold for life, and the light side too hot, so everything would have to live in the middle, which would still get a sufficient amount of light.

"Another argument along the same lines is that the range of vision under water is habitually much smaller than on dry land, but that has not stopped vision developing under water; quite the opposite. "

Up to a point, since animals in sediment-heavy rivers tend to lose their sight. The visibility in the Amazon is something like 5 feet, so maybe that's the threshold for blindness.

Could your animals have evolved in a small sea loaded with sediment from rivers dumping into it?

it could, but that wouldn't stop it from developing eyes on land. In at least one instance (pit vipers) terrestrial organisms have evolved photoreceptors. Therefore, it's plausible to presume an organism can still evolve eyes even after they've gotten on land. On a planet where no land organisms have eyes, the ones with eyes will surely quickly dominate

>On a planet where no land organisms have eyes, the ones with eyes will surely quickly dominate

assuming there's nothing better. on a planet where you have echolocators or electric-sensings (dolphins and electric eels, say)...exactly what advantage do you get from having a scallop or frog eye? (you can be stunned without being able to see your predator, no matter how good your eye is)

@rodlox Good point, I had thought of that, but I have some trouble believing echolocation would arise before eyes. That being said, it's not all too improbable, I could definitely see it happening now that I've thought more about it.

Spugpow: the fact that river dolphins tend to lose sight is a good argument that there is lower limit of visibility below which vision is not useful. The original supposition by Barlowe was that such a state could exist over an entire planet, which seems near-impossible to me.

Mike & Rodlox: On Earth vision seems to have taken off extremely quickly. In fact, the Cambrium explosion is now thought to have been due to the rapid evolution of vision. What no-one knows is whether there were animals with echolocation before that. I doubt it. That means there is no analogue on Earth for well-established echolocation followed by the evolution of a primitive eye (as far as I know). Would a primitive eye be useful enough to keep evolving under such circumstances. I recognised that problem in my post when I wrote "I doubt eye evolution would really be held back by superior senses, already present, but that line of thought deserves further thought." The answer may lie in the relative strengths and weaknesses of vision and echolocation. That is a good subject for a post, but one that deserves study beforehand. Don't expect it any time soon...

there might be one very good reason why heat sensors did not evolve especially during the cambrium explosion:there was nothing to detect!every creature at that time had the same temperature than the surrounding environment... sure enough their muscles and metabolism produced some small amount of heat but it dispersed immediately leaving nothing to detect...near infrared now is something different but why stop there if there are other wavelengths to "see"?as long as they are reflected by other objects and i doubt that heat is reflected in a needed amount...

even nowadays heat detection alone would be pretty dangerous for an agile creature because there are lots of obstacles/objects even other beasts not producing any form of infrared radiation or reflecting it which would not be "seen".even modern nightvision devices use very often an infrared source to "light up" the surroundings in order to actually have something to detect.

i just recently read an article about giant squids living in the depths of the oceans in absolute darkness... they have the biggest eyes known!it is thought that their eyes are very sensitive and even detect the smallest amount of disturbance in the darkness produced by bioluminescent algae when a pray or their predator, the sperm whale is floating through the water.

life has a tendency to use any source of information it can get hold of - any - because it is an advantage over the others!

Those are good points; when considering arguments for the superiority of vision of other senses, I considered hearing and sonar, and came up with a similar set of weaknesses of hearing as compared to vision. Obviously, the strengths and weaknesses do not overlap completely, which is why mutltiple senses are useful.